Our long term goal is to understand the neural basis of complex form vision as it operates under natural viewing conditions. Decades of vision research using simple stimuli and controlled viewing conditions have produced sophisticated models of processing in the early visual system. We propose to evaluate these models directly by recording responses under conditions simulating natural vision. In Aim 1 we propose to acquire data in area V1 using both naturalistic and more standard conventional stimuli. Quantitative methods will be used to estimate cells' spatio-temporal filtering properties from these data. The experiments and analyses will reveal how are V1 represents and processes information during natural vision. They will also reveal how these functions differ from those predicted from experiments using conventional simple stimuli. In Aim 2, we will evaluate a range of functional computational models of area V1 to identify those models that can account for responses observed during simulated natural vision. This will be accomplished by direct statistical comparison between models. Successful completion of this Aim will result in the first computational model(s) that can account for the spatio-temporal responses of V1 neurons during natural vision. In Aim 3 we will assess the modulatory influence of extra-retinal factors such as attention during simulated natural vision. We propose to do this by combining standard match-to-sample behavioral tasks with our naturalistic stimuli and our quantitative receptive field estimation methods. This will provide a sensitive measure of potential extra-retinal effects in area V1. Experiments on natural vision are important because they will allow us to evaluate our current theories of human visual cortical function and identify areas in which our understanding is weak. They will also allow us to address complex aspects of form vision that cannot easily be approached using more conventional methods.